1. Field of the Invention
The present invention relates to magnetic heads, and in particular relates to a magnetic head for use in VTR equipment and a tape storage device such as a DDS (digital data storage, digital tape streamer).
2. Description of the Related Art
In a magnetic head for use in VTR equipment, the track width has been decreased year after year in consistency with the recording density improvement and the digitizing a signal recording pattern.
From such a background, an MIG (metal in gap) type magnetic head has been used, in which a pair of magnetic core half-pieces, which are made of ferrite or ceramic so as to have metallic magnetic thin films formed thereon and being excellent in soft magnetic characteristics, are integrated together with an insulating film therebetween by a bonding member such as deposited glass.
Recently, in order to reduce the track width further than that of the MIG type magnetic head, a thin-film magnetic head having a thin-film coil is tried to incorporate it into a magnetic head for VTR equipment.
FIG. 13 shows a perspective view of a thin-film magnetic head 200 as an example of a magnetic head. The thin-film magnetic head 200 is built by bonding side faces of plate-like core half-pieces 202 and 203 together with a core-embedded layer 205 therebetween so as to have a plate-like integrated structure on the whole. The core half-pieces 202 and 203 are made of a hardwearing ceramic material such as CaTiO3 and AlTiC (Al2O3—TiO2 ceramic), or Ni—Zn ferrite.
As shown in FIG. 13, one surface of the thin-film magnetic head 200 is also shaped like a slender convex curved surface so as to have a medium sliding surface 210, and on both sides of the medium sliding surface 210 in the width direction, steps 212 and 213 are continuously formed so as to sandwich the medium sliding surface 210. That is, in an upper portion of the half-pieces 202 and 203, a projection 215 cramped by the steps 212 and 213 is constructed, and the top surface of the projection 215 constitutes the medium sliding surface 210 while surfaces neighboring both the side surfaces of the medium sliding surface 210 in the width direction constitute side faces 207 and 207.
A medium sliding surface 210 is to be a curved surface (a curved surface along a sliding direction of a recording medium) along a circular arc with a radius of curvature R on a surface including large side surfaces 202a and 203a of the core half-pieces 202 and 203 and furthermore, the medium sliding surface 210 is to be a curved surface along a circular arc with a radius of curvature r existing on a side face 202b (a surface perpendicularly neighboring on the side surface 202a) of the core half-piece 202.
The radius of curvature r is set to be smaller than the radius of curvature R, and is also set to be substantially constant along a longitudinal direction of the medium sliding surface 210. For example, if in the core half-pieces 202 and 203, the width is 1.0 mm, the height is 1.8 mm, the depth is 0.28 mm, and the with of the medium sliding surface 210 is between from 150 to 200 μm, the radius of curvature R can be between from 3 to 5 mm, and the radius of curvature r can be between from 1 to 2 mm.
The core-embedded layer 205 arranged at the center of the medium sliding surface 210 is provided with a magnetic head 211 built therein, and at the substantial center of the medium sliding surface 210, a magnetic gap G of the magnetic head 211 is exposed.
In the thin-film magnetic head 200 mentioned above, the radius of curvature r is set to be substantially constant along a longitudinal direction of the medium sliding surface 210, so that the width of an actual contact part with a recording medium of the medium sliding surface 210 is substantially constant along a longitudinal direction (a sliding direction of a recording medium) of the medium sliding surface 210.
Therefore, during the traveling of a medium, a foreign material, for example, adhering to a tape-shaped recording medium is readily caught up between the medium sliding surface 210 and the recording medium, possibly resulting in damage of the medium sliding surface 210 due to the foreign material.
In order to prevent the damage of the medium sliding surface 210, the contact part with a recording medium of the medium sliding surface 210 may be reduced by tapering the medium sliding surface 210 with the radius of curvature r reduced to be as small as possible; however, in this case, there is a problem that the contact pressure of the recording medium is concentrated on an edge extremity of the medium sliding surface 210 so that the abrasion of the medium sliding surface 210 is increased.